A number of studies have shown that deaf patients can get help in communicating by presenting components of speech as patterns of skin stimulation.
Single channel devices have been found particularly useful in presenting the rhythm, stress and duration patterns of speech (Erber, N. P. 1978--International Journal of Rehabilitaton Research, Vol. 1 Pages 27-37 entitled "Vibratory Perception by Deaf Children"; Plant, G. L. 1979--Australian Journal of Audiology, Vol. 1 Pages 76-82 entitled "Use of Tactile Supplements in the Rehabilitation of the Deafened--a case study"; Proctor, A. 1982--Proceedings of the Second National Child Development Conference Melbourne August 1982 entitled "Effects of tactual aid on language comprehension of pre-lingual profoundly deaf children"; Plant, G. L. & Risberg, A. 1983--Speech Transmission Laboratories Quarterly Progress Report Vol. 2-3 Pages 61-84 entitled "The Transmission of Fundamental Variations via a Single Channel Vibrotactile Aid"). Multi-channel devices have been able to convey information that is especially important in identifying vowels, consonants and words (Pickett, J. M. & Pickett, B. H. 1963--Journal of Speech and Hearing Research Number 6 Pages 207-222 entitled--Communication of Speech Sounds of a Tactual Vocoder; Saunders, F. A. 1973--Proceedings in the Fourth Annual Meeting of the Bio-Medical Engineering Socieity, Los Angeles, Calif. entitled--"Electrotactile Sensory Aids for the Handicapped"; Kirman, J. H. 1974--Journal of the Acoustic Society of America Number 55 Pages 163-169 entitled--"Tactual Perception of Computer derived format deafness from voiced speech"; Engelmann, S. and Rosov, R. J. 1975--Journal of Exceptional Children Number 41 Pages 245-253 entitled--"Tactual Hearing Experiment with Deaf and Hearing Subjects; Spens, K. E. 1980--Speech Transmission Laboratories Quarterly Progress Report Number 4 Pages 23-39 entitled--"Tactile Speech Communication Aids for the Deaf"; Sparks, D. W., Kuhl, P. K., Edmonds, A. E. & Gray, G. P. 1978--Journal of the Acoustic Society of America Number 63 Pages 246-257 entitled--"Investigating the Mesa (Electrotactile Speech Aid: the transmission of segmental figures of speech); Reed, C. M., Durlach, N. I. & Braida, L. D., 1978--A.S.H.A. American Speech and Hearing Association Monograph Number 20 entitled "Research on Communication and Speech: a review"; Traunmuller, H. 1980--Journal of Communication Disorders Number 13 Pages 183-193 entitled "Sentiphone: a tactual speech communication aid"). Most tactile vocoders have stimulated the skin by mechanical vibration on body loci such as the forearm and the fingertips. This has been carried out by using solenoids, other electromagnetically operated units or piezo-electric devices. Electrotactile stimulation has been carried out by delivering electric current to the skin receptors and nerve endings, primarily around the abdomen but also the forearm and the fingertips.
Many of the studies have been carried out in the laboratory as they have been research based requiring the use of bench top equipment. It has been acknowledged that further progress will require more portable units that will enable studies in the field and allow the patients to learn to use them most of the time. This goal has been achieved with a single channel vibratory device (Plant) but still has not been possible for either vibratory or electrotactile multichannel skin stimulus units. Mechanical vibrators are large and have a high power consumption requiring a number of batteries. Electrotactile stimulation using an array of surface electrodes requires less power and is lightweight and compact. A problem with electrical stimulation of the skin receptors and nerve endings, however, is that the dynamic range for electric current is small and the sensation is not pleasant and frequently described as prickly. Research conducted by the applicant has confirmed the value of a simple single channel vibratory device. It has also shown that with electrical stimulation, moving patterns can be detected which have similar time courses to the frequency transitions of consonants which suggests that an appropriate unit could be helpful in understanding speech.
As a result, a stimulus unit presenting speech by electrotactile stimulation employing the electrical principles used by Saunders was constructed. In addition, two electrode arrays with matrices of 8.times.8 electrodes have been developed. The system can allow different speech processing strategies to be evaluated on deaf patients. Psychophysical tests have confirmed the small dynamic range between threshold and pain and have shown that some subjects experience an unpleasant prickly sensation within the operating range.